The article presents the results of the studies of corrosion activity of water produced from the White Tiger, White Rabbit and Dragon oilfields operated by Vietsovpetro JV. Produced water in Vietsovpetro is a mixture of formation water and treated seawater used for waterflooding. There are substantial differences in chemical composition and content of corrosive components in water between different oilfields and even within one oilfield. Maturing of the oilfields leads to an increase in water cuts and in aggressive components content in produced water.
Oil gathering pipelines and oil processing equipment are made of ASTM A106, API 5X carbon steels. In Vietsovpetro the pipes and equipment made of carbon steels have been used successfully for more than 25 years, but in recent years corrosion damage was noticed on the inner surfaces of the pipes the oil gathering and transportation system. It was found that the present rate of corrosion of carbon steel in the conditions at which the system of gathering and transportation of the gas-liquid products operates (45 °С, 0.1 MPa) is 0.22-0.31 mm per year. At elevated pressures and temperatures (120 °С, 10 MPa) the corrosion rates increase to 0.26-0.64 mm per year. Corrosion aggressiveness of produced water is caused primarily by carbon dioxide, water and solid particles. The results of inspection of pipelines wall thickness after corrosive impact prove the high aggressive activity of produced water. Electrochemical corrosion that causes local defects (blisters) on the inner surface of the oil pipelines, transporting produced fluids with high water content, is caused primarily by formation of a separate water phase in the pipes and by presence of aggressive components in water.
A field trial of corrosion inhibitor injection into the gathering and transportation system was performed to reduce the internal corrosion. It was found that in presence of corrosion inhibitor the rate of corrosion lowers from 0.31 to 0.052 mm per year.
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